Band-pass filter

ABSTRACT

A band-pass filter includes an unbalanced port, a first balanced port, a second balanced port, and first to third resonators provided between the unbalanced port and the first and second balanced ports. The second resonator and the third resonator each are a resonator with both ends open. The second resonator and the third resonator are adjacent to each other in a circuit configuration, and electromagnetically coupled by magnetic coupling as main coupling. The first resonator is provided closer to the second resonator than to the third resonator, and jump-coupled to the third resonator.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.17/242,053, filed Apr. 27, 2021, the contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a balanced band-pass filter thatincludes an unbalanced port and a pair of balanced ports.

2. Description of the Related Art

As a kind of electronic components that can be used in transmission andreception circuits of wireless communication devices such as cellularphones or wireless LAN communication devices, there are band-passfilters each including a plurality of resonators. The band-pass filterpreferably has an attenuation pole at which insertion loss abruptlyvaries in each of a first vicinity range and a second vicinity range.The first vicinity range is a frequency range lower than a pass band andin the vicinity of the pass band. The second vicinity range is afrequency range higher than the pass band and in the vicinity of thepass band.

As the band-pass filters, balanced band-pass filters each including apair of balanced ports as output ports are known. The balanced band-passfilter is required to have a good amplitude balance characteristic and agood phase balance characteristic. The good amplitude balancecharacteristic means that two balanced element signals that constitute abalanced signal outputted from the band-pass filter have an amplitudedifference of approximately zero. The good phase balance characteristicmeans that the two balanced element signals have a phase difference ofapproximately 180 degrees.

JP 2002-374139 A discloses a balanced LC filter including a pair ofbalanced input terminals and a pair of balanced output terminals. In thebalanced LC filter, an attenuation pole is provided on a lower frequencyside or a higher frequency side than a center frequency of the balancedLC filter using pole adjustment capacitors.

JP 2007-267264 A discloses a lumped constant bandpass filter including apair of balanced terminals and an unbalanced terminal. JP 2007-267264 Adescribes that an unbalanced-input-and-balanced-output filter isconfigured by using the unbalanced terminal as an input terminal andusing the pair of balanced terminals as output terminals.

Mobile communication systems up to the fourth generation are put topractical use at present. Standardization of fifth-generation mobilecommunication systems is now underway. In these mobile communicationsystems, it has been difficult for conventional balanced band-passfilters to form an abrupt attenuation pole in each of the foregoingfirst and second vicinity ranges while satisfying the balancecharacteristics.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a balanced band-passfilter, including an unbalanced port and a pair of balanced ports, thatcan form an abrupt attenuation pole while satisfying a balancecharacteristic.

A band-pass filter according to the present invention includes anunbalanced port, a first balanced port, a second balanced port, andfirst to third resonators provided between the unbalanced port and thefirst and second balanced ports in a circuit configuration. The secondresonator and the third resonator each are a resonator with both endsopen. The second resonator and the third resonator are adjacent to eachother in the circuit configuration, and electromagnetically coupled bymagnetic coupling as main coupling. The first resonator is providedcloser to the second resonator than to the third resonator in thecircuit configuration, and jump-coupled to the third resonator.

In the band-pass filter according to the present invention, the firstresonator may be a resonator with one end shorted, and provided betweenthe unbalanced port and the second resonator in the circuitconfiguration.

In the band-pass filter according to the present invention, a distancebetween the second resonator and the third resonator may be shorter thana distance between the first resonator and the second resonator.

The band-pass filter according to the present invention may furtherinclude a fourth resonator provided between the unbalanced port and thefirst and second balanced ports in the circuit configuration. In thiscase, the fourth resonator may be provided closer to the third resonatorthan to the second resonator in the circuit configuration, andjump-coupled to the second resonator. In this case, the first resonatormay be a resonator with one end shorted, and provided between theunbalanced port and the second resonator in the circuit configuration.The fourth resonator may be a resonator with both ends open, andprovided between the first and second balanced ports and the thirdresonator in the circuit configuration.

If the band-pass filter according to the present invention is providedwith the fourth resonator, the distance between the second resonator andthe third resonator may be shorter than that between the first resonatorand the second resonator, and shorter than that between the thirdresonator and the fourth resonator.

The band-pass filter according to the present invention may furtherinclude a stack to integrate at least the second and third resonators.The stack may include a plurality of stacked dielectric layers, aplurality of stacked conductor layers, and a plurality of through holes.In such a case, the plurality of conductor layers may include aplurality of resonator-forming conductor layers. The plurality ofthrough holes may include a plurality of resonator-forming throughholes. Each of the second and third resonators may include a firstthrough hole line, a second through hole line, and a conductor layerportion. Each of the first and second through hole lines may be formedof serially connected two or more through holes of the plurality ofresonator-forming through holes, and may penetrate two or moredielectric layers of the plurality of dielectric layers. The conductorlayer portion may be formed of one or more resonator-forming conductorlayers of the plurality of resonator-forming conductor layers, and mayconnect one end of the first through hole line to one end of the secondthrough hole line.

The band-pass filter according to the present invention includes thefirst to third resonators. The second resonator and the third resonatorare adjacent to each other in the circuit configuration, andelectromagnetically coupled by magnetic coupling as main coupling. Thefirst resonator is provided closer to the second resonator than to thethird resonator in the circuit configuration, and jump-coupled to thethird resonator. Therefore, according to the present invention, it ispossible to provide the band-pass filter that can form an abruptattenuation pole while satisfying a balance characteristic.

Other and further objects, features and advantages of the presentinvention will appear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing the circuit configuration of aband-pass filter according to a first embodiment of the invention.

FIG. 2 is a perspective view showing the band-pass filter according tothe first embodiment of the invention.

FIG. 3 is a perspective view showing the band-pass filter according tothe first embodiment of the invention.

FIG. 4 is a perspective view showing the interior of the band-passfilter shown in FIG. 2 and FIG. 3 .

FIG. 5A and FIG. 5B are explanatory diagrams showing respectivepatterned surfaces of first and second dielectric layers of the stack ofthe band-pass filter shown in FIG. 2 and FIG. 3 .

FIG. 6A and FIG. 6B are explanatory diagrams showing respectivepatterned surfaces of third and fourth dielectric layers of the stack ofthe band-pass filter shown in FIG. 2 and FIG. 3 .

FIG. 7A and FIG. 7B are explanatory diagrams showing respectivepatterned surfaces of fifth and sixth dielectric layers of the stack ofthe band-pass filter shown in FIG. 2 and FIG. 3 .

FIG. 8A and FIG. 8B are explanatory diagrams showing respectivepatterned surfaces of seventh and eighth dielectric layers of the stackof the band-pass filter shown in FIG. 2 and FIG. 3 .

FIG. 9A is an explanatory diagram showing a patterned surface of each ofa ninth to an eighteenth dielectric layer of the stack of the band-passfilter shown in FIG. 2 and FIG. 3 .

FIG. 9B is an explanatory diagram showing a patterned surface of each ofa nineteenth and a twentieth dielectric layer of the stack of theband-pass filter shown in FIG. 2 and FIG. 3 .

FIG. 10A is an explanatory diagram showing a patterned surface of eachof a twenty-first and a twenty-second dielectric layer of the stack ofthe band-pass filter shown in FIG. 2 and FIG. 3 .

FIG. 10B is an explanatory diagram showing a patterned surface of atwenty-third dielectric layer of the stack of the band-pass filter shownin FIG. 2 and FIG. 3 .

FIGS. 11A and 11B are explanatory diagrams showing respective patternedsurfaces of twenty-fourth and twenty-fifth dielectric layers of thestack of the hand-pass filter shown in FIG. 2 and FIG. 3 .

FIG. 12 is a characteristic diagram showing the pass characteristics ofa first model of a hand-pass filter.

FIG. 13 is a characteristic diagram showing the pass characteristics ofa second model of the band-pass filter.

FIG. 14 is a characteristic diagram showing the pass characteristics ofa third model of the band-pass filter.

FIG. 15 is a characteristic diagram showing the pass characteristics ofa fourth model of the band-pass filter.

FIG. 16 is a characteristic diagram showing the pass characteristics ofa fifth model of the band-pass filter.

FIG. 17 is a characteristic diagram showing an example of passcharacteristic of the band-pass filter according to the first embodimentof the invention.

FIG. 18 is a characteristic diagram showing a portion of FIG. 17 on anenlarged scale.

FIG. 19 is a characteristic diagram showing an example of amplitudebalance characteristic of the band-pass filter according to the firstembodiment of the invention.

FIG. 20 is a characteristic diagram showing an example of phase balancecharacteristic of the band-pass filter according to the first embodimentof the invention.

FIG. 21 is a characteristic diagram showing an example of reflectioncharacteristic of the unbalanced port of the band-pass filter accordingto the first embodiment of the invention.

FIG. 22 is a characteristic diagram showing an example of passcharacteristic of the first and second balanced ports of the band-passfilter according to the first embodiment of the invention.

FIG. 23 is a circuit diagram showing the circuit configuration of aband-pass filter according to a second embodiment of the invention.

FIG. 24 is a perspective view showing the interior of the hand-passfilter according to the second embodiment of the invention.

FIG. 25A and FIG. 25B are explanatory diagrams showing respectivepatterned surfaces of first and second dielectric layers of the stack ofthe band-pass filter according to the second embodiment of theinvention.

FIG. 26A and FIG. 26B are explanatory diagrams showing respectivepatterned surfaces of third and fourth dielectric layers of the stack ofthe band-pass filter according to the second embodiment of theinvention.

FIG. 27A and FIG. 27B are explanatory diagrams showing respectivepatterned surfaces of fifth and sixth dielectric layers of the stack ofthe band-pass filter according to the second embodiment of theinvention.

FIG. 28A is an explanatory diagram showing a patterned surface of eachof a seventh and a eighth dielectric layer of the stack of the band-passfilter according to the second embodiment of the invention.

FIG. 28B is an explanatory diagram showing a patterned surface of aninth dielectric layer of the stack of the band-pass filter according tothe second embodiment of the invention.

FIG. 29A is an explanatory diagram showing a patterned surface of atenth dielectric layer of the stack of the band-pass filter according tothe second embodiment of the invention.

FIG. 29B is an explanatory diagram showing a patterned surface of eachof a eleventh and a sixteenth dielectric layer of the stack of theband-pass filter according to the second embodiment of the invention.

FIG. 30A is an explanatory diagram showing a patterned surface of eachof a seventeenth and a eighteenth dielectric layer of the stack of theband-pass filter according to the second embodiment of the invention.

FIG. 30B is an explanatory diagram showing a patterned surface of eachof a nineteenth and a twentieth dielectric layer of the stack of theband-pass filter according to the second embodiment of the invention.

FIG. 31A and FIG. 31B are explanatory diagrams showing respectivepatterned surfaces of twenty-first and twenty-second dielectric layersof the stack of the band-pass filter according to the second embodimentof the invention.

FIG. 32A and FIG. 32B are explanatory diagrams showing respectivepatterned surfaces of twenty-third and twenty-fourth dielectric layersof the stack of the band-pass filter according to the second embodimentof the invention.

FIG. 33 is a characteristic diagram showing an example of passcharacteristic of the band-pass filter according to the secondembodiment of the invention.

FIG. 34 is a characteristic diagram showing a portion of FIG. 33 on anenlarged scale.

FIG. 35 is a characteristic diagram showing an example of amplitudebalance characteristic of the band-pass filter according to the secondembodiment of the invention.

FIG. 36 is a characteristic diagram showing an example of phase balancecharacteristic of the band-pass filter according to the secondembodiment of the invention,

FIG. 37 is a characteristic diagram showing an example of reflectioncharacteristic of the unbalanced port of the band-pass filter accordingto the second embodiment of the invention.

FIG. 38 is a characteristic diagram showing an example of passcharacteristic of the first and second balanced ports of the band-passfilter according to the second embodiment of the invention.

FIG. 39 is a circuit diagram showing the circuit configuration of aband-pass filter according to a third embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Preferred embodiments of the present invention will now be described indetail with reference to the drawings. First, reference is made to FIG.1 to describe the circuit configuration of a band-pass filter accordingto the first embodiment of the invention. FIG. 1 shows the circuitconfiguration of the band-pass filter according to the presentembodiment. As shown in FIG. 1 , a band-pass filter 1 includes anunbalanced port 11, a first balanced port 12, a second balanced port 13,a port 14, a first resonator 21, a second resonator 22, a thirdresonator 23, and a fourth resonator 24.

The first to fourth resonators 21 to 24 are provided between theunbalanced port 11 and the first and second balanced ports 12 and 13 inthe circuit configuration. The second resonator 22 and the thirdresonator 23 are adjacent to each other in the circuit configuration.The first resonator 21 is provided closer to the second resonator 22than to the third resonator 23 in the circuit configuration. The fourthresonator 24 is provided closer to the third resonator 23 than to thesecond resonator 22 in the circuit configuration. In the presentapplication, the expression of “in the(a) circuit configuration” is usedto indicate not layout in physical configuration but layout in thecircuit diagram.

Specifically in the present embodiment, the first to fourth resonators21 to 24 are provided in this order from the side of the unbalanced port11. That is, the second resonator 22 is provided closer to theunbalanced port 11 than the third resonator 23 in the circuitconfiguration. The first resonator 21 is provided between the unbalancedport 11 and the second resonator 22 in the circuit configuration. Thefourth resonator 24 is provided between the first and second balancedports 12 and 13 and the third resonator 23 in the circuit configuration.

The first resonator 21 is a resonator with one end shorted. Theband-pass filter 1 further includes capacitors C1 and C11. The capacitorC1 connects one end of the first resonator 21 to a ground. The capacitorC11 connects the one end of the first resonator 21 to the unbalancedport 11. The other end of the first resonator 21 is connected to theground.

The second to fourth resonators 22 to 24 each are a resonator with bothends open. The band-pass filter 1 further includes capacitors C2A, C2B,C3A, C3B, C4A, and C4B. The capacitor C2A connects one end of the secondresonator 22 to the ground. The capacitor C2B connects the other end ofthe second resonator 22 to the ground. The capacitor C3A connects oneend of the third resonator 23 to the ground. The capacitor C3B connectsthe other end of the third resonator 23 to the ground. The capacitor C4Aconnects one end of the fourth resonator 24 to the ground. The capacitorC4B connects the other end of the fourth resonator 24 to the ground.

The band-pass filter 1 further includes capacitors C12, C23A, C23B,C34A, and C34B. The capacitor C12 connects the one end of the firstresonator 21 to the one end of the second resonator 22. The capacitorC23A connects the one end of the second resonator 22 to the one end ofthe third resonator 23. The capacitor C23B connects the other end of thesecond resonator 22 to the other end of the third resonator 23. Thecapacitor C34A connects the one end of the third resonator 23 to the oneend of the fourth resonator 24. The capacitor C34B connects the otherend of the third resonator 23 to the other end of the fourth resonator24.

The first balanced port 12 is connected to the one end of the fourthresonator 24. The second balanced port 13 is connected to the other endof the fourth resonator 24.

The second resonator 22 and the third resonator 23 are magneticallycoupled, and also capacitively coupled through the capacitors C23A andC23B. In FIG. 1 , a curve indicated with a symbol M represents themagnetic coupling between the second resonator 22 and the thirdresonator 23. Here, out of magnetic coupling and capacitive couplingthat contribute to electromagnetic coupling between two resonators,relatively strong coupling is referred to as main coupling, and theother is referred to as sub coupling. Specifically in the presentembodiment, the second resonator 22 and the third resonator 23 areelectromagnetically coupled by the magnetic coupling as the maincoupling and the capacitive coupling as the sub coupling.

The first resonator 21 and the second resonator 22 are magneticallycoupled, and also capacitively coupled through the capacitor C12.Specifically in the present embodiment, the first resonator 21 and thesecond resonator 22 are electromagnetically coupled by the capacitivecoupling as the main coupling and the magnetic coupling as the subcoupling.

The third resonator 23 and the fourth resonator 24 are magneticallycoupled, and also capacitively coupled through the capacitors C34A andC34B. Specifically in the present embodiment, the third resonator 23 andthe fourth resonator 24 are electromagnetically coupled by thecapacitive coupling as the main coupling and the magnetic coupling asthe sub coupling.

The first resonator 21 is magnetically coupled to the third resonator23, which is not adjacent to the first resonator 21 in the circuitconfiguration. The fourth resonator 24 is magnetically coupled to thesecond resonator 22, which is not adjacent to the fourth resonator 24 inthe circuit configuration. Electromagnetic coupling between tworesonators that are not adjacent to each other in a circuitconfiguration is referred to as jump-coupling. In FIG. 1 , curvesindicated with a symbol Mc represent the magnetic coupling between thetwo resonators that are not adjacent to each other in the circuitconfiguration.

The operation of the band-pass filter 1 will now be described. Theband-pass filter 1 is a band-pass filter the pass band of which ispredetermined. The band-pass filter 1 is a so-called balanced band-passfilter. The band-pass filter 1 is configured so that an unbalancedsignal is received at and outputted from the unbalanced port 11, a firstbalanced element signal is received at and outputted from the firstbalanced port 12, and a second balanced element signal is received atand outputted from the second balanced port 13. The first balancedelement signal and the second balanced element signal constitute abalanced signal. The band-pass filter 1 converts between balanced andunbalanced signals.

Next, a structure of the band-pass filter 1 will be described withreference to FIGS. 2 to 4 . FIGS. 2 and 3 are perspective views of theband-pass filter 1. FIG. 4 is a perspective view showing the interior ofthe band-pass filter 1. The band-pass filter 1 further includes a stack30 for integrating the ports 11 to 13, the first to fourth resonators 21to 24, and the capacitors C1, C2A, C2B, C3A, C3B, C4A, C4B, C11, C12,C23A, C23B, C34A and C34B. Although details will be described later, thestack 30 includes a plurality of stacked dielectric layers, a pluralityof stacked conductor layers, and a plurality of through holes.

The stack 30 is shaped like a rectangular solid. The stack 30 includes atop surface 30A, a bottom surface 30B, and four side surfaces 30C to30F, which constitute the periphery of the stack 30. The top surface 30Aand the bottom surface 30B are opposite each other. The side surfaces30C and 30D are opposite each other. The side surfaces 30E and 30F areopposite each other. The side surfaces 30C to 30F are perpendicular tothe top surface 30A and the bottom surface 30B. In the stack 30, theplurality of dielectric layers and the plurality of conductor layers arestacked in the direction perpendicular to the top surface 30A and thebottom surface 30B. This direction will be referred to as the stackingdirection. The stacking direction is shown by the arrow T in FIG. 2 toFIG. 4 . The top surface 30A and the bottom surface 30B are located atopposite ends in the stacking direction T.

Here, X, Y, and Z directions are defined as shown in FIGS. 2 to 4 . TheX, Y, and Z directions are orthogonal to one another. In the presentembodiment, a direction parallel to the stacking direction T will bereferred to as the Z direction. The opposite directions to the X, Y, andZ directions are defined as −X, −Y, and −Z directions, respectively.

As shown in FIGS. 2 and 3 , the top surface 30A is located at the end ofthe stack 30 in the −Z direction. The bottom surface 30B is located atthe end of the stack 30 in the direction. The side surface 30C islocated at the end of the stack 30 in the −X direction. The side surface30D is located at the end of the stack 30 in the X direction. The sidesurface 30E is located at the end of the stack 30 in the −Y direction.The side surface 30F is located at the end of the stack 30 in the Ydirection.

The band-pass filter 1 further includes first to eighth terminals 111,112, 113, 114, 115, 116, 117, and 118. The first terminal 111 is locatedto extend from the top surface 30A to the bottom surface 30B via theside surface 30C. The first terminal 112 is located to extend from thetop surface 30A to the bottom surface 30B via the side surface 30D. Eachof the third to fifth terminals 113 to 115 is located to extend from thetop surface 30A to the bottom surface 30B via the side surface 30E. Thethird to fifth terminals 113 to 115 are arranged in this order in the Xdirection. Each of the sixth to eighth terminals 116 to 118 is locatedto extend from the top surface 30A to the bottom surface 30B via theside surface 30F. The sixth to eighth terminals 116 to 118 are arrangedin this order in the X direction.

The first terminal 111 corresponds to the unbalanced port 11. The fifthterminal 115 corresponds to the second balanced port 13. The eighthterminal 118 corresponds to the first balanced port 12. The fourthterminal 114 corresponds to the second balanced port 13. Each of thethird, fourth, sixth and seventh terminals 113, 114, 116 and 117 isconnected to the ground.

The stack 30 will be described in detail with reference to FIG. 5A toFIG. 11B. The multilayer stack 30 includes twenty-six dielectric layersstacked on each other. The twenty-six dielectric layers will be referredto as the first to twenty-sixth dielectric layers in the order frombottom to top. The first to twenty-sixth dielectric layers will bedenoted by the reference numerals 31 to 56.

FIG. 5A shows the patterned surface of the first dielectric layer 31.FIG. 5A shows terminal parts 111 a to 118 a constituting parts of theterminals 111 to 118, respectively.

FIG. 5B shows the patterned surface of the second dielectric layer 32. Aground conductor layers 321 and 322 are formed on the patterned surfaceof the dielectric layer 32. The conductor layer 321 is connected to thefourth and seventh terminals 114 and 117. The conductor layer 322 isconnected to the third and sixth terminals 113 and 116.

FIG. 6A shows the patterned surface of the third dielectric layer 33. Aconductor layers 331, 332, 333 and 334 are formed on the patternedsurface of the dielectric layer 33. The conductor layer 333 is connectedto the eighth terminal 118. The conductor layer 334 is connected to thefifth terminal 115.

FIG. 6B shows the patterned surface of the fourth dielectric layer 34. Aconductor layers 341, 342, 343 and 344 are formed on the patternedsurface of the dielectric layer 34. Further, through holes 34T1, 34T2,34T3 and 34T4 are formed in the dielectric layer 34. The through holes34T1, 34T2, 34T3 and 34T4 are connected to the conductor layers 341,342, 343 and 344, respectively.

FIG. 7A shows the patterned surface of the fifth dielectric layer 35. Aconductor layer 351 is formed on the patterned surface of the dielectriclayer 35. Further, through holes 35T1, 35T2, 35T3, 35T4 and 35T5 areformed in the dielectric layer 35. The through holes 34T1, 34T2, 34T3and 34T4 formed in the fourth dielectric layer 34 are connected to thethrough holes 35T1, 35T2, 35T3 and 35T4, respectively. The through hole35T5 is connected to the conductor layer 351.

FIG. 7B shows the patterned surface of the sixth dielectric layer 36. Aconductor layer 361 is formed on the patterned surface of the dielectriclayer 36. Further, through holes 36T1, 36T2, 36T3, 36T4, 36T5 and 36T6are formed in the dielectric layer 36. The through holes 35T1, 35T2,35T3, 35T4 and 35T5 formed in the fifth dielectric layer 35 areconnected to the through holes 36T1, 36T2, 36T3, 36T4 and 36T5,respectively. The through hole 36T6 is connected to the conductor layer361.

FIG. 8A shows the patterned surface of the seventh dielectric layer 37.A conductor layer 371 is formed on the patterned surface of thedielectric layer 37. Further, through holes 37T1, 37T2, 37T3, 37T4, 37T5and 37T6 are formed in the dielectric layer 37. The through holes 36T1,36T2, 36T3, 36T4 and 36T6 formed in the sixth dielectric layer 36 areconnected to the through holes 37T1, 37T2, 37T3, 37T4 and 37T6,respectively. The through hole 37T5 and the through hole 36T5 formed inthe dielectric layer 36 are connected to the conductor layer 371.

FIG. 8B shows the patterned surface of the eighth dielectric layer 38. Aconductor layer 381 is formed on the patterned surface of the dielectriclayer 38. The conductor layer 381 is connected to the first terminal111. Further, through holes 38T1, 38T2, 38T3, 38T4 and 38T5 are formedin the dielectric layer 38. The through holes 37T1, 37T2, 37T3, 37T4 and37T5 formed in the seventh dielectric layer 37 are connected to thethrough holes 38T1, 38T2, 38T3, 38T4 and 38T5, respectively. The throughhole 37T6 formed in the seventh dielectric layer 37 is connected to theconductor layer 381.

FIG. 9A shows the patterned surface of each of the ninth to eighteenthdielectric layers 39 to 48. In each of the dielectric layers 39 to 48,there are formed through holes 39T1, 39T2, 39T3, 39T4 and 39T5. Thethrough holes 38T1, 38T2, 38T3, 38T4 and 38T5 formed in the eighthdielectric layer 38 are connected to the through holes 39T1, 39T2, 39T3,39T4 and 39T5 formed in the ninth dielectric layer 39, respectively. Inthe dielectric layers 39 to 48, every vertically adjacent through holesdenoted by the same reference signs are connected to each other.

FIG. 9B shows the patterned surface of each of the nineteenth andtwentieth dielectric layers 49 and 50. A resonator-forming conductorlayer 491 is formed on the patterned surface of each of the dielectriclayers 49 and 50. The resonator-forming conductor layer 491 is connectedto the fifth and eighth terminals 115 and 118. Further, in each of thedielectric layers 49 and 50, there are formed through holes 49T1, 49T2,49T3, 49T4 and 49T5. The through holes 39T1, 39T2, 39T3, 39T4 and 39T5formed in the eighteenth dielectric layer 48 are connected to thethrough holes 49T1, 49T2, 49T3, 49T4 and 49T5 formed in the nineteenthdielectric layer 49, respectively. In the dielectric layers 49 and 50,every vertically adjacent through holes denoted by the same referencesigns are connected to each other.

FIG. 10A shows the patterned surface of each of the twenty-first andtwenty-second dielectric layers 51 and 52. In each of the dielectriclayers 51 and 52, there are formed through holes 51T1, 51T2, 51T3, 51T4and 51T5. The through holes 49T1, 49T2, 49T3, 49T4 and 49T5 formed inthe twentieth dielectric layer 50 are connected to the through holes51T1, 51T2, 51T3, 51T4 and 51T5 formed in the twenty-first dielectriclayer 51, respectively. In the dielectric layers 51 and 52, everyvertically adjacent through holes denoted by the same reference signsare connected to each other.

FIG. 10B shows the patterned surface of the twenty-third dielectriclayer 53. A resonator-forming conductor layer 531 is formed on thepatterned surface of the dielectric layer 53. The resonator-formingconductor layer 531 is connected to the third and sixth terminals 113and 116. Further, through holes 53T1, 53T2, 53T3, 53T4 and 53T5 areformed in the dielectric layer 53. The through holes 51T1, 51T2, 51T3and 51T4 formed in the twenty-second dielectric layer 52 are connectedto the through holes 53T1, 53T2, 53T3 and 53T4, respectively. Thethrough hole 53T5 and the through hole 51T5 formed in the twenty-seconddielectric layer 52 are connected to part of the resonator-formingconductor layer 531, i.e. a portion including the middle of theresonator-forming conductor layer 531 in a longitudinal direction.

FIG. 11A shows the patterned surface of the twenty-fourth dielectriclayer 54. Resonator-forming conductor layers 541, 542 and 543 are formedon the patterned surface of the dielectric layer 54. Theresonator-forming conductor layer 541 is connected to the third andsixth terminals 113 and 116. The through hole 53T5 formed in thetwenty-third dielectric layer 53 is connected to part of theresonator-forming conductor layer 541, i.e. a portion including themiddle of the resonator-forming conductor layer 541 in the longitudinaldirection. Each of the resonator-forming conductor layers 542 and 543has a first end and a second end opposite to each other.

Further, through holes 54T1, 54T2, 54T3 and 54T4 are formed in thedielectric layer 54. The through hole 54T1 and the through hole 53T1formed in the dielectric layer 53 are connected to a portion of theresonator-forming conductor layers 542 near the first end thereof. Thethrough hole 54T2 and the through hole 53T2 formed in the dielectriclayer 53 are connected to a portion of the resonator-forming conductorlayers 542 near the second end thereof. The through hole 54T3 and thethrough hole 53T3 formed in the dielectric layer 53 are connected to aportion of the resonator-forming conductor layers 543 near the first endthereof. The through hole 54T4 and the through hole 53T4 formed in thedielectric layer 53 are connected to a portion of the resonator-formingconductor layers 543 near the second end thereof.

FIG. 11B shows the patterned surface of the twenty-fifth dielectriclayer 55. Resonator-forming conductor layer 552 and 553 are formed onthe patterned surface of the dielectric layer 55. Each of theresonator-forming conductor layers 552 and 553 has a first end and asecond end opposite to each other. The through hole 54T1 formed in thedielectric layer 54 is connected to a portion of the resonator-formingconductor lavers 552 near the first end thereof. The through hole 54T2formed in the dielectric layer 54 is connected to a portion of theresonator-forming conductor layers 552 near the second end thereof. Thethrough hole 54T3 formed in the dielectric layer 54 is connected to aportion of the resonator-forming conductor layers 553 near the first endthereof. The through hole 54T4 formed in the dielectric layer 54 isconnected to a portion of the resonator-forming conductor layers 553near the second end thereof.

Although it is not shown in the drawing, a mark may be formed in thepatterned surface of the twenty-sixth dielectric layer 56.

The stack 30 shown in FIGS. 2 and 3 is formed by stacking the first totwenty-sixth dielectric layers 31 to 56 such that the patterned surfaceof the first dielectric layer 31 serves as the bottom surface 30B of thestack 30 and the surface of the twenty-sixth dielectric layer 56opposite to the patterned surface thereof serves as the top surface 30Aof the stack 30. The first to eighth terminals 111 to 118 are thenformed on the periphery of the stack 30, whereby the band-pass filter 1shown in FIGS. 2 and 3 is completed.

A correspondence between the components of the band-pass filter 1 andthe components inside the stack 30 shown in FIGS. 5A to 11B will bedescribed below. The plurality of the dielectric lavers of the stack 30include the plurality of resonator-forming conductor layers 491, 531,541, 542, 543, 552, and 553 to constitute the first to fourth resonators21 to 24. The plurality of through holes of the stack 30 include aplurality of resonator-forming through holes to constitute the first tofourth resonators 21 to 24.

The first resonator 21 is formed of the resonator-forming conductorlayers 531 and 541, the through holes 35T5, 36T5, 37T5, 38T5 and 53T5,the through hole 39T5 formed in each of the dielectric layer 39 to 48,the through hole 49T5 formed in each of the dielectric layer 49 and 50,and the through hole 51T5 formed in each of the dielectric layers 51 and52.

The second resonator 22 is formed of the resonator-forming conductorlayers 542 and 552, the through holes 34T1, 34T2, 35T1, 35T2, 36T1,36T2, 37T1, 37T2, 38T1, 38T2, 53T1 and 53T2, the through holes 39T1 and39T2 formed in each of the dielectric layer 39 to 48, the through holes49T1 and 49T2 formed in each of the dielectric layer 49 and 50, and thethrough holes 51T1 and 51T2 formed in each of the dielectric layers 51and 52.

As shown in FIG. 4 , the second resonator 22 includes a first throughhole line 22A, a second through hole line 22B, and a conductor layerportion 22C. The first through hole line 22A is formed of the throughholes 34T1, 35T1, 36T1, 37T1, 38T1, and 53T1, the through holes 39T1formed in each of the dielectric layers 39 to 48, the through holes 49T1formed in each of the dielectric layers 49 and 50, and the through holes51T1 formed in each of the dielectric layers 51 and 52 connected inseries. The first through hole line 22A penetrates the dielectric layers34 to 53.

The second through hole line 22B is formed of the through holes 34T2,35T2, 36T2, 37T2, 38T2, and 53T2, the through holes 39T2 formed in eachof the dielectric layers 39 to 48, the through holes 49T2 formed in eachof the dielectric layers 49 and 50, and the through holes 51T2 formed ineach of the dielectric layers 51 and 52 connected in series. The secondthrough hole line 22B penetrates the dielectric layers 34 to 53.

The conductor layer portion 22C is formed of the resonator-formingconductor layers 542 and 552 that are connected to each other via thethrough holes 54T1 and 54T2. The conductor layer portion 22C connectsone end of the first through hole line 22A to one end of the secondthrough hole line 22B.

The third resonator 23 is formed of the resonator-forming conductorlayers 543 and 553, the through holes 34T3, 34T4, 35T3, 35T4, 36T3,36T4, 37T3, 37T4, 38T3, 38T4, 53T3, 53T4, 54T3, and 54T4, the throughholes 39T3 and 39T4 formed in each of the dielectric layer 39 to 48, thethrough holes 49T3 and 49T4 formed in each of the dielectric layer 49and 50, and the through holes 51T3 and 51T4 formed in each of thedielectric layers 51 and 52.

As shown in FIG. 4 , the third resonator 23 includes a first throughhole line 23A, a second through hole line 23B, and a conductor layerportion 23C. The first through hole line 23A is formed of the throughholes 34T3, 35T3, 36T3, 37T3, 38T3, and 53T3, the through holes 39T3formed in each of the dielectric layers 39 to 48, the through holes 49T3formed in each of the dielectric layers 49 and 50, and the through holes51T3 formed in each of the dielectric layers 51 and 52 connected inseries. The first through hole line 23A penetrates the dielectric layers34 to 53.

The second through hole line 23B is formed of the through holes 34T4,35T4, 36T4, 37T4, 38T4, and 53T4, the through holes 39T4 formed in eachof the dielectric layers 39 to 48, the through holes 49T4 formed in eachof the dielectric layers 49 and 50, and the through holes 51T4 formed ineach of the dielectric layers 51 and 52 connected in series. The secondthrough hole line 23B penetrates the dielectric layers 34 to 53.

The conductor layer portion 23C is formed of the resonator-formingconductor layers 543 and 553 that are connected to each other via thethrough holes 54T3 and 54T4. The conductor layer portion 22C connectsone end of the first through hole line 23A to one end of the secondthrough hole line 23B.

The fourth resonator 24 is formed of the resonator-forming conductorlayer 491 formed in each of the dielectric layer 49 and 50.

The capacitor C1 is formed of the conductor layers 322 and 351, and thedielectric layers 32 to 34 interposed between the conductor layers 322and 351.

The capacitor C2A is formed of the conductor layers 321 and 341, and thedielectric layers 32 and 33 interposed between the conductor layers 321and 341. The capacitor C2B is formed of the conductor layers 321 and342, and the dielectric layers 32 and 33 interposed between theconductor layers 321 and 342.

The capacitor C3A is formed of the conductor layers 321 and 343, and thedielectric layers 32 and 33 interposed between the conductor layers 321and 343. The capacitor C3B is formed of the conductor layers 321 and344, and the dielectric layers 32 and 33 interposed between theconductor layers 321 and 344.

The capacitor C4A is formed of the conductor layers 321 and 333, and thedielectric layer 32 interposed between the conductor lavers 321 and 333.The capacitor C4B is formed of the conductor layers 321 and 334, and thedielectric layer 32 interposed between the conductor layers 321 and 334.

The capacitor C11 is formed of the conductor layers 351, 361, 371 and381, the dielectric layer 35 interposed between the conductor layers 351and 361, the dielectric layer 36 interposed between the conductor layers361 and 371, and the dielectric layer 37 interposed between theconductor layers 371 and 381. The capacitor C12 is formed of theconductor layers 341 and 351, and the dielectric layer 34 interposedbetween the conductor layers 341 and 351.

The capacitor C23A is formed of the conductor layers 331, 341 and 343,and the dielectric layer 33 interposed between the conductor layer 331and the conductor layers 341 and 343. The capacitor C23B is formed ofthe conductor layers 332, 342 and 344, and the dielectric layer 33interposed between the conductor layer 332 and the conductor layers 342and 344.

The capacitor C34A is formed of the conductor layers 333 and 343, andthe dielectric layer 33 interposed between the conductor layers 333 and343. The capacitor C34B is formed of the conductor layers 334 and 344,and the dielectric layer 33 interposed between the conductor layers 334and 344.

Next, structural features of the band-pass filter 1 will be described.As shown in FIG. 4 , the distance between the second resonator 22 andthe third resonator 23 is shorter than that between the first resonator21 and the second resonator 22, and is shorter than that between thethird resonator 23 and the fourth resonator 24.

As shown in FIG. 9B, the resonator-forming conductor layer 491 formed inthe dielectric layer 49 and the resonator-forming conductor layer 491formed in the dielectric layer 50 are located so as to overlap eachother when viewed from the Z direction. As shown in FIGS. 10B and 11A,the resonator-forming conductor layer 531 formed in the dielectric layer53 and the resonator-forming conductor layer 541 formed in thedielectric layer 54 are located so as to overlap each other when viewedfrom the Z direction. As shown in FIGS. 11A and 11B, theresonator-forming conductor layer 542 formed in the dielectric layer 54and the resonator-forming conductor layer 552 formed in the dielectriclayer 55 are located so as to overlap each other when viewed from the Zdirection. The resonator-forming conductor layer 543 formed in thedielectric layer 54 and the resonator-forming conductor layer 553 formedin the dielectric layer 55 are located so as to overlap each other whenviewed from the Z direction.

As described above, in the band-pass filter 1 according to the presentembodiment, the second resonator 22 and the third resonator 23 areelectromagnetically coupled by the magnetic coupling as the maincoupling. The first resonator 21 is jump-coupled to the third resonator23. The fourth resonator 24 is jump-coupled to the second resonator 22.According to the present embodiment, these couplings can form anattenuation pole at which insertion loss abruptly varies in each of afirst vicinity range that is a frequency range lower than the pass bandand in the vicinity of the pass band and a second vicinity range that isa frequency range higher than the pass band and in the vicinity of thepass band.

The attenuation pole will be hereinafter described with reference tosimulation results. In simulation, first to fifth models of a band-passfilter having the same circuit configuration as that of the band-passfilter 1 of the present embodiment were used. In the simulation, theband-pass filter was designed so as to have a pass band between 3.3 and3.9 GHz. In the simulation, the pass characteristic of the band-passfilter was represented using a mixed mode S parameter, which representeda response of a difference signal between first and second balancedelement signals outputted from the first and second balanced ports 12and 13 when an unbalanced signal was inputted to the unbalanced port 11.The S parameter is hereinafter referred to as insertion loss.

Here, a symbol k23 represents a magnetic coupling coefficient betweenthe second resonator 22 and the third resonator 23. A symbol k13represents a magnetic coupling coefficient of the jump-coupling betweenthe first resonator 21 and the third resonator 23. A symbol k24represents a magnetic coupling coefficient of the jump-coupling betweenthe second resonator 22 and the fourth resonator 24. In the first tofifth models, each of the magnetic coupling coefficients k23, k13, andk24 varied from each other. In the simulation, the pass characteristicof each of the first to fifth models as obtained.

First, the pass characteristic of each of the first and second modelswill be described. In the first model, the magnetic coupling coefficientk23 was set at 0.37, and the magnetic coupling coefficients k13 and k24of the jump-coupling each were set at 0. In the second model, themagnetic coupling coefficient k23 was set at 0.07, and the magneticcoupling coefficients k13 and k24 of the jump-coupling each were set at0.

FIG. 12 shows the pass characteristic of the first model. FIG. 13 showsthe pass characteristic of the second model. In each of FIGS. 12 and 13, the horizontal axis represents frequency, and the vertical axisrepresents insertion loss. It is found from FIG. 12 that in a case wherethe second resonator 22 and the third resonator 23 areelectromagnetically coupled by the magnetic coupling as the maincoupling with the increased magnetic coupling coefficient k23, anattenuation pole is formed in a frequency range higher than the passband of the band-pass filter.

It is also found from FIG. 13 that when the second resonator 22 and thethird resonator 23 are electromagnetically coupled by the capacitivecoupling as the main coupling with the decreased magnetic couplingcoefficient k23, an attenuation pole is formed in a frequency rangelower than the pass band of the band-pass filter.

In general, in a band-pass filter constituted by two resonators, it isknown that when a magnetic coupling coefficient between the tworesonators relatively increases and a coupling capacitance between thetwo resonators relatively decreases, an attenuation pole is formed in afrequency range higher than a center frequency of a pass band of theband-pass filter. In the first and second models, the magnetic couplingcoefficients k13 and k24 of the jump-coupling are set at 0, in order toclarify a variation of the attenuation pole due to difference in theelectromagnetic coupling between the second resonator 22 and the thirdresonator 23. However, the foregoing explanation of the variation of theattenuation pole holds true for the magnetic coupling coefficients k13and k24 having a value other than 0. In the present embodiment, asdescribed above, the electromagnetic coupling between the secondresonator 22 and the third resonator 23 by the magnetic coupling as themain coupling allows formation of the attenuation pole in the secondvicinity range.

Next, the pass characteristic of the third model will be described. Inthe third model, the magnetic coupling coefficient k23 was set at 0.37.The magnetic coupling coefficient k13 of jump-coupling was 0.032, andthe magnetic coupling coefficient k24 of the jump-coupling was set at 0.

FIG. 14 shows the pass characteristic of the third model. In FIG. 14 ,the horizontal axis represents frequency, and the vertical axisrepresents insertion loss. It is found from FIG. 14 and the passcharacteristic of the first model (the magnetic coupling coefficientsk13 and k24 of the jump-coupling each are 0) shown in FIG. 12 that anattenuation pole is formed in a frequency range lower than the pass bandof the band-pass filter, due to the jump-coupling between the firstresonator 21 and the third resonator 23. In the present embodiment, asdescribed above, the jump-coupling between the third resonator 23 andthe first resonator 21 allows formation of the attenuation pole in thefirst vicinity range.

Next, the pass characteristic of the fourth model will be described. Inthe fourth model, the magnetic coupling coefficient k23 was set at 0.37.The magnetic coupling coefficient k13 of jump-coupling was 0, and themagnetic coupling coefficient k24 of the jump-coupling was set at 0.02.

FIG. 15 shows the pass characteristic of the fourth model. In FIG. 15 ,the horizontal axis represents frequency, and the vertical axisrepresents insertion loss. It is found from FIG. 15 and the passcharacteristic of the first model (the magnetic coupling coefficientsk13 and k24 of the jump-coupling each are 0) shown in FIG. 12 that anattenuation pole is formed in a frequency range lower than the pass bandof the band-pass filter, due to the jump-coupling between the secondresonator 22 and the fourth resonator 24. In the present embodiment, asdescribed above, the jump-coupling between the fourth resonator 24 andthe second resonator 22 allows formation of the attenuation pole in thefirst vicinity range.

Next, the pass characteristic of the fifth model will be described. Inthe fifth model, the magnetic coupling coefficient k23 was set at 0.37.The magnetic coupling coefficient k13 of jump-coupling was 0.032, andthe magnetic coupling coefficient k24 of the jump-coupling was set at0.02.

FIG. 16 shows the pass characteristic of the fifth model. In FIG. 16 ,the horizontal axis represents frequency, and the vertical axisrepresents insertion loss. It is found from FIG. 16 , the passcharacteristic of the third model (the magnetic coupling coefficient k24is 0) shown in FIG. 14 , and the pass characteristic of the fourth model(the magnetic coupling coefficient k13 is 0) shown in FIG. 15 , thatattenuation pole formed by the jump-coupling of the two pairs ofresonators becomes abrupter than the attenuation pole formed by thejump-coupling of the one pair of resonators shown in FIGS. 14 and 15 .This is because of synergy between the effect of the jump-coupling ofone pair of resonators and the effect of the jump-coupling of the otherpair of resonators. In the present embodiment, the jump-coupling of thetwo pairs of resonators makes the attenuation pole formed in the firstvicinity range abrupter.

As is understood from the simulation results shown in FIGS. 12 to 16 ,according to the present embodiment, it is possible to form an abruptattenuation pole in each of the first and second vicinity ranges, withthe use of the magnetic coupling between the second resonator 22 and thethird resonator 23 as the main coupling and the use of at least one ofthe jump-coupling between the first resonator 21 and the third resonator23 and the jump-coupling between the second resonator 22 and the fourthresonator 24. In the present embodiment, it is possible to form anabrupter attenuation pole in the first vicinity range, with the use ofboth of the jump-coupling between the first resonator 21 and the thirdresonator 23 and the jump-coupling between the second resonator 22 andthe fourth resonator 24.

In the present embodiment, the distance between the second resonator 22and the third resonator 23 is made shorter than that between the firstresonator 21 and the second resonator 22, and shorter than that betweenthe third resonator 23 and the fourth resonator 24. Specifically in thepresent embodiment, the capacitive coupling between the second resonator22 and the third resonator 23 is made relatively strong while themagnetic coupling between the second resonator 22 and the thirdresonator 23 is made relatively strong by making the distance betweenthe second resonator 22 and the third resonator 23 relatively short.Thus, the attenuation pole formed in the second vicinity range has afrequency close to the pass band. Therefore, according to the presentembodiment, it is possible to achieve a characteristic for abruptlyvarying the insertion loss in the vicinity of the pass band. Note that asecond embodiment will describe an example in which the distance betweenthe second resonator 22 and the third resonator 23 is made longer thanthat of the present embodiment.

According to the present embodiment, it is possible to form theattenuation pole as described above while satisfying balancecharacteristics. This effect will be described later with reference toan example of characteristic of the band-pass filter 1.

In the present embodiment, each of the second to fourth resonators 22 to24 is a resonator with both ends open. The resonator with both ends openis able to have a symmetrical circuit configuration with respect to thecenter of the resonator. As shown in FIG. 1 , the present embodiment hasa symmetrical circuit configuration in which a group of the capacitorsC2A, C3A, C4A, C23A, and C34A and a group of the capacitors C2B, C3B,C4B, C23B, and C34B are symmetrical with respect to the second to fourthresonators 22 to 74.

Respective ends of the resonator with both ends open are referred to asa first end and a second end. In the resonator with both ends open, whenthe balance of an electric field and a magnetic field between the sideof the first end and the side of the second end is lost, the balancecharacteristics deteriorate. In the present embodiment, providing thefourth resonator 24 improves the symmetry of the circuit configurationof the band-pass filter 1, as compared with the case of having no fourthresonator 24. Therefore, according to the present embodiment, it ispossible to improve the balance characteristics by relieving unbalanceof the electric field and the magnetic field.

Next, examples of characteristics of the band-pass filter 1 according tothe present embodiment will be described with reference to FIGS. 17 to22 . Here, the examples of characteristics of the band-pass filter 1that is designed such that the pass band includes a frequency band of3.3 GHz to 3.9 GHz will be described.

FIG. 17 shows an example of pass characteristic of the band-pass filter1. FIG. 18 shows part of FIG. 17 on an enlarged scale. Here, theforegoing insertion loss is indicated as the pass characteristic of theband-pass filter 1. In each of FIGS. 17 and 18 , the horizontal axisrepresents frequency, and the vertical axis represents insertion loss.It is found from FIG. 17 that in the band-pass filter 1, an attenuationpole at which the insertion loss abruptly varies is formed in each offirst and second vicinity ranges.

The insertion loss is preferably 2.5 dB or less. As shown in FIG. 18 ,the band-pass filter 1 has the insertion loss of 2.5 dB or less in theforegoing frequency bands.

FIG. 19 shows an example of amplitude balance characteristic of theband-pass filter 1. The amplitude balance characteristic of theband-pass filter 1 is represented here using a difference in amplitudebetween the first and second balanced element signals outputted from thefirst and second balanced ports 12 and 13 upon input of an unbalancedsignal to the unbalanced port 11, which will hereinafter be simplyreferred to as the amplitude difference. The amplitude difference isexpressed in positive values when the amplitude of the first balancedelement signal is greater than the amplitude of the second balancedelement signal, and in negative values when the amplitude of the firstbalanced element signal is smaller than the amplitude of the secondbalanced element signal. In FIG. 19 , the horizontal axis representsfrequency, and the vertical axis represents amplitude difference. Withthe amplitude difference denoted as in (dB), in preferably has a valueof −1.5 or more and not more than 1.5, and more preferably −1.0 or moreand not more than 1.0. As shown in FIG. 19 , the band-pass filter 1 hasan m value of −1.0 or more and not more than 1.0 in the foregoingfrequency band.

FIG. 20 shows an example of phase balance characteristic of theband-pass filter 1. The phase balance characteristic of the band-passfilter 1 is represented here using a difference in phase between thefirst and second balanced element signals outputted from the first andsecond balanced ports 12 and 13 upon input of an unbalanced signal tothe unbalanced port 11, which will hereinafter be simply referred to asthe phase difference. The phase difference represents the magnitude ofadvancement of the phase of the first balanced element signal relativeto the phase of the second balanced element signal. In FIG. 20 , thehorizontal axis represents frequency, and the vertical axis representsphase difference. With the phase difference denoted as p (deg), ppreferably has a value of 165 or more and not more than 196. As shown inFIG. 20 , the band-pass filter 1 has a p value of 165 or more and notmore than 195 in the foregoing frequency band.

FIG. 21 shows an example of reflection characteristic of the unbalancedport 11 of the band-pass filter 1. FIG. 22 shows an example ofreflection characteristic of the first and second balanced ports 12 and13 of the band-pass filter 1. In each of FIGS. 21 and 22 , thehorizontal axis represents frequency, and the vertical axis representsreturn loss. The return loss is preferably 10 dB or more. As shown inFIGS. 21 and 22 , the band-pass filter 1 has the return loss of 10 dB ormore in the foregoing frequency band.

As described above, the band-pass filter 1 having the characteristicsshown in FIGS. 17 to 22 is usable in at least the frequency band of 3.3GHz to 3.9 GHz, and has the favorable balance characteristics in thisfrequency band. As is understood from FIGS. 17 to 22 , the band-passfilter 1 can form the abrupt attenuation pole in each of the first andsecond vicinity ranges while satisfying the balance characteristics.

Second Embodiment

A second embodiment of the invention will now be described. First, thecircuit configuration of a band-pass filter according to the presentembodiment will be described in brief with reference to FIG. 23 . FIG.23 shows the circuit configuration of the band-pass filter according tothe present embodiment.

The circuit configuration of a band-pass filter 101 according to thepresent embodiment is different from that of the band-pass filter 1according to the first embodiment in the following respect. In thepresent embodiment, there is no capacitor C23B provided for connectingone end of the second resonator 22 on the side of the capacitor C2B toone end of the third resonator 23 on the side of the capacitor C3B. Theother circuit configuration of the band-pass filter 101 is the same asthat of the band-pass filter 1 according to the first embodiment.

Next, a structure of the band-pass filter 101 will be described. FIG. 24is a perspective view showing the interior of the band-pass filter 101.Just as with the band-pass filter 1 according to the first embodiment,the band-pass filter 101 includes the stack 30 and the first to eightsterminals 111 to 118 (refer to FIGS. 2 and 3 ). The stack 30 of thepresent embodiment integrates the ports 11 to 13, the first to fourthresonators 21 to 24, and the capacitors C1, C2A, C2B, C3A, C3B, C4A,C4B, C11, C12, C23A, C34A, and C34B. The shape and layout of the firstto eighth terminals 111 to 118 are the same as those of the firstembodiment.

The stack 30 of the present embodiment will be described in detail withreference to FIG. 25A to FIG. 32B. In the present embodiment, the stack30 includes stacked twenty-five dielectric layers instead of thedielectric layers 31 to 56 of the first embodiment. The twenty-fivedielectric layers will be referred to as the first to twenty-fifthdielectric layers in the order from bottom to top. The first totwenty-fifth dielectric layers will be denoted by the reference numerals61 to 85.

FIG. 25A shows the patterned surface of the first dielectric layer 61.FIG. 25A shows terminal parts 111 a to 118 a constituting parts of theterminals 111 to 118, respectively.

FIG. 25B shows the patterned surface of the second dielectric layer 62.A ground conductor layer 621 is formed on the patterned surface of thedielectric layer 62. The conductor layer 621 is connected to the fourthand seventh terminals 114 and 117.

FIG. 26A shows the patterned surface of the third dielectric layer 63. Aconductor layer 631 is formed on the patterned surface of the dielectriclayer 63. Further, through hole 63T5 is formed in the dielectric layer63. The through hole 6315 is connected to the conductor layer 631.

FIG. 26B shows the patterned surface of the fourth dielectric layer 64.A conductor layers 641, 642 and 643 are formed on the patterned surfaceof the dielectric layer 63. The through hole 63T5 formed in the thirddielectric layer 63 is connected to the conductor layer 641. Theconductor layer 632 is connected to the eighth terminal 118. Theconductor layer 633 is connected to the fifth terminal 115.

FIG. 27A shows the patterned surface of the fifth dielectric layer 65. Aconductor layers 651, 652, 653 and 654 are formed on the patternedsurface of the dielectric layer 65. Further, through holes 65T1, 65T2,65T3 and 65T4 are formed in the dielectric layer 65. The through holes65T1, 65T2, 65T3 and 651 are connected to the conductor layers 651, 652,653 and 654, respectively,

FIG. 27B shows the patterned surface of the sixth dielectric layer 66. Aconductor layer 661 is formed on the patterned surface of the dielectriclayer 66. Further, through holes 66T1, 66T2, 66T3, 66T4 and 66T5 areformed in the dielectric layer 66. The through holes 65T1, 65T2, 65T3and 65T4 formed in the fifth dielectric layer 65 are connected to thethrough holes 66T1, 66T2, 66T3 and 66T4, respectively. The through hole6615 is connected to the conductor layer 661.

FIG. 28A shows the patterned surface of each of the seventh and eighthdielectric layers 67 and 68. In each of the dielectric layers 67 and 68,there are formed through holes 67T1, 67T2, 67T3, 67T4 and 67T5. Thethrough holes 66T1, 66T2, 66T3, 66T4 and 66T5 formed in the sixthdielectric layer 66 are connected to the through holes 67T1, 67T2, 67T3,67T4 and 67T5 formed in the seventh dielectric layer 67, respectively.In the dielectric layers 67 and 68, every vertically adjacent throughholes denoted by the same reference signs are connected to each other.

FIG. 28B shows the patterned surface of the ninth dielectric layer 69. Aconductor layer 691 is formed on the patterned surface of the dielectriclayer 69. Further, through holes 69T1, 69T2, 69T3, 69T4 and 69T5 areformed in the dielectric layer 69. The through holes 67T1, 67T2, 67T3,67T4 and 67T5 formed in the eighth dielectric layer 68 are connected tothe through holes 69T1, 69T2, 69T3, 69T4 and 69T5, respectively.

FIG. 29A shows the patterned surface of the tenth dielectric layer 70. Aconductor layer 701 is formed on the patterned surface of the dielectriclayer 70. Further, through holes 70T1, 70T2, 70T3, 70T4 and 70T5 areformed in the dielectric layer 70. The through holes 69T1, 69T2, 69T3and 69T4 formed in the ninth dielectric layer 69 are connected to thethrough holes 70T1, 70T2, 70T3 and 70T4, respectively. The through hole70T5 and the through hole 69T5 formed in the ninth dielectric layer 69are connected to the conductor layer 701.

FIG. 29A shows the patterned surface of each of the eleventh tosixteenth dielectric layers 71 to 76. In each of the dielectric layers71 to 76, there are formed through holes 71T1, 71T2, 71T3, 71T4 and71T5. The through holes 70T1, 70T2, 70T3, 70T4 and 70T5 formed in thetenth dielectric layer 70 are connected to the through holes 71T1, 71T2,71T3, 71T4 and 71T5 formed in the eleventh dielectric layer 71,respectively. In the dielectric layers 71 to 76, every verticallyadjacent through holes denoted by the same reference signs are connectedto each other.

FIG. 30A shows the patterned surface of each of the seventeenth andeighteenth dielectric layers 77 and 78. A resonator-forming conductorlayer 771 is formed on the patterned surface of each of the dielectriclayers 77 and 78. The resonator-forming conductor layer 771 is connectedto the fifth and eighth terminals 115 and 118. Further, in each of thedielectric lavers 77 and 78, there are formed through holes 77T1, 77T2,77T3, 77T4 and 77T5. The through holes 71T1, 71T2, 71T3, 71T4 and 7115formed in the sixteenth dielectric layer 76 are connected to the throughholes 77T1, 77T2, 77T3, 77T4 and 77T5 formed in the seventeenthdielectric layer 77, respectively. In the dielectric layers 77 and 78,every vertically adjacent through holes denoted by the same referencesigns are connected to each other.

FIG. 30B shows the patterned surface of each of the nineteenth andtwentieth dielectric layers 79 and 80. In each of the dielectric layers77 and 87, there are formed through holes 79T1, 79T2, 79T3, 79T4 and79T5. The through holes 77T1, 77T2, 77T3, 77T4 and 77T5 formed in theeighteenth dielectric layer 78 are connected to the through holes 79T1,79T2, 79T3, 79T4 and 79T5 formed in the nineteenth dielectric layer 79,respectively. In the dielectric layers 79 and 80, every verticallyadjacent through holes denoted by the same reference signs are connectedto each other.

FIG. 31A shows the patterned surface of the twenty-first dielectriclayer 81. A resonator-forming conductor layer 811 is formed on thepatterned surface of the dielectric layer 81. The resonator-formingconductor layer 811 is connected to the third and sixth terminals 113and 116. Further, through holes 81T1, 81T2, 81T3, 81T4 and 81T5 areformed in the dielectric layer 81. The through holes 79T1, 79T2, 79T3and 79T4 formed in the twentieth dielectric layer 70 are connected tothe through holes 81T1, 81T2, 81T3 and 81T4, respectively.

FIG. 31B shows the patterned surface of the twenty-second dielectriclayer 54. A resonator-forming conductor layer 821 is formed on thepatterned surface of the dielectric layer 82. The resonator-formingconductor layer 821 is connected to the third and sixth terminals 113and 116. The through hole 81T5 formed in the twenty-first dielectriclayer 81 is connected to part of the resonator-forming conductor layer821, i.e. a portion including the middle of the resonator-formingconductor layer 821 in a longitudinal direction. Further, through holes82T1, 82T2, 82T3, 82T4 and 82T5 are formed in the dielectric layer 82.The through holes 81T1, 81T2, 81T3 and 81T4 formed in the dielectriclayer 81 are connected to the through holes 82T1, 82T2, 82T3 and 82T4,respectively.

FIG. 32A shows the patterned surface of the twenty-third dielectriclayer 83. Resonator-forming conductor layers 832 and 833 are formed onthe patterned surface of the dielectric layer 83. Each of theresonator-forming conductor layers 832 and 833 has a first end and asecond end opposite to each other. Further, through holes 83T1, 83T2,83T3 and 83T4 are formed in the dielectric layer 83. The through hole83T1 and the through hole 82T1 formed in the twenty-second dielectriclayer 82 are connected to a portion of the resonator-forming conductorlayers 832 near the first end thereof. The through hole 83T2 and thethrough hole 82T2 formed in the dielectric layer 82 are connected to aportion of the resonator-forming conductor layers 832 near the secondend thereof. The through hole 83T3 and the through hole 82T3 formed inthe dielectric layer 82 are connected to a portion of theresonator-forming conductor layers 833 near the first end thereof. Thethrough hole 83T4 and the through hole 82T4 formed in the dielectriclayer 82 are connected to a portion of the resonator-forming conductorlayers 833 near the second end thereof.

FIG. 32B shows the patterned surface of the twenty-fourth dielectriclayer 84. Resonator-forming conductor layer 842 and 843 are formed onthe patterned surface of the dielectric layer 84. Each of theresonator-forming conductor layers 842 and 843 has a first end and asecond end opposite to each other. The through hole 83T1 formed in thetwenty-third dielectric layer 83 is connected to a portion of theresonator-forming conductor layers 842 near the first end thereof. Thethrough hole 83T2 formed in the dielectric layer 83 is connected to aportion of the resonator-forming conductor layers 842 near the secondend thereof. The through hole 83T3 formed in the dielectric layer 83 isconnected to a portion of the resonator-forming conductor layers 843near the first end thereof. The through hole 83T4 formed in thedielectric layer 83 is connected to a portion of the resonator-formingconductor layers 843 near the second end thereof.

Although it is not shown in the drawing, a mark may be formed in thepatterned surface of the twenty-fifth dielectric layer 85.

The stack 30 of the present embodiment is formed by stacking the firstto twenty-fifth dielectric layers 61 to 85 such that the patternedsurface of the first dielectric layer 61 serves as the bottom surface30B of the stack 30 (see FIGS. 2 and 3 ) and the surface of thetwenty-sixth dielectric layer 85 opposite to the patterned surfacethereof serves as the top surface 30A of the stack 30 (see FIGS. 2 and 3). The first to eighth terminals 111 to 118 are then formed on theperiphery of the stack 30, whereby the band-pass filter 101 iscompleted.

A correspondence between the components of the band-pass filter 101 andthe components inside the stack 30 shown in FIGS. 25A to 32B will bedescribed below.

The first resonator 21 is formed of the resonator-forming conductorlayers 811 and 821, the through holes 70T5 and 81T5, the through hole71T5 formed in each of the dielectric layer 71 to 76, the through hole77T5 formed in each of the dielectric layer 77 and 78, and the throughhole 79T5 formed in each of the dielectric layers 79 and 80.

The second resonator 22 is formed of the resonator-forming conductorlayers 832 and 842, the through holes 65T1, 65T2, 66T1, 66T2, 69T1,69T2, 70T1, 70T2, 81T1, 81T2, 82T1, 82T2, 83T1 and 83T2, the throughholes 67T1 and 67T2 formed in each of the dielectric layer 67 and 68,the through holes 71T1 and 71T2 formed in each of the dielectric layer71 to 76, the through holes 77T1 and 77T2 formed in each of thedielectric layer 77 and 78, and the through holes 79T1 and 79T2 formedin each of the dielectric lavers 79 and 80.

Like the first embodiment, the second resonator 22 includes a firstthrough hole line 22A, a second through hole line 22B, and a conductorlayer portion 22C (see FIG. 24 ). The first through hole line 22A isformed of the through holes 65T1, 66T1, 69T1, 70T1, 81T1, and 82T1, thethrough holes 67T1 formed in each of the dielectric layers 67 and 68,the through holes 71T1 formed in each of the dielectric layers 71 to 76,the through holes 77T1 formed in each of the dielectric layers 77 and78, and the through holes 79T1 formed in each of the dielectric layers79 and 80 connected in series. The first through hole line 22Apenetrates the dielectric layers 65 to 82.

The second through hole line 22B is formed of the through holes 65T2,66T2, 69T2, 70T2, 81T2, and 82T2, the through holes 67T2 formed in eachof the dielectric layers 67 and 68, the through holes 71T2 formed ineach of the dielectric layers 71 to 76, the through holes 77T2 formed ineach of the dielectric layers 77 and 78, and the through holes 79T2formed in each of the dielectric layers 79 and 80 connected in series.The first through hole line 22A penetrates the dielectric layers 65 to82.

The conductor layer portion 22C is formed of the resonator-formingconductor layers 832 and 842 that are connected to each other via thethrough holes 83T1 and 83T2.

The third resonator 23 is formed of the resonator-forming conductorlayers 833 and 843, the through holes 65T3, 65T4, 66T3, 66T4, 69T3,69T4, 70T3, 70T4, 81T3, 81T4, 82T3, 82T4, 83T3, and 83T4, the throughholes 67T3 and 67T4 formed in each of the dielectric layer 67 and 68,the through holes 71T3 and 71T4 formed in each of the dielectric layer71 to 76, the through holes 77T3 and 77T4 formed in each of thedielectric layer 77 and 78, and the through holes 79T3 and 79T4 formedin each of the dielectric layers 79 and 80.

Like the first embodiment, the third resonator 23 includes a firstthrough hole line 23A, a second through hole line 23B, and a conductorlayer portion 23C (see FIG. 24 ). The first through hole line 23A isformed of the through holes 65T3, 66T3, 69T3, 70T3, 81T3, and 82T3, thethrough holes 67T3 formed in each of the dielectric layers 67 and 68,the through holes 71T3 formed in each of the dielectric layers 71 to 76,the through holes 77T3 formed in each of the dielectric layers 77 and78, and the through holes 79T3 formed in each of the dielectric layers79 and 80 connected in series. The first through hole line 22Apenetrates the dielectric layers 65 to 82.

The second through hole line 23B is formed of the through holes 65T4,66T4, 69T4, 70T4, 81T4, and 82T4, the through holes 67T4 formed in eachof the dielectric layers 67 and 68, the through holes 71T4 formed ineach of the dielectric layers 71 to 76, the through holes 77T4 formed ineach of the dielectric layers 77 and 78, and the through holes 79T4formed in each of the dielectric layers 79 and 80 connected in series.The first through hole line 22A penetrates the dielectric layers 65 to82.

The conductor layer portion 23C is formed of the resonator-formingconductor layers 833 and 843 that are connected to each other via thethrough holes 83T3 and 83T4.

The fourth resonator 24 is formed of the resonator-forming conductorlayer 771 formed in each of the dielectric layer 77 and 78.

The capacitor C1 is formed of the conductor layers 621 and 701, and thedielectric layers 62 to 69 interposed between the conductor layers 621and 701.

The capacitor C2A is formed of the conductor layers 621 and 651, and thedielectric layers 62 to 64 interposed between the conductor layers 621and 651. The capacitor C2B is formed of the conductor layers 621 and651, and the dielectric layers 62 to 64 interposed between the conductorlayers 621 and 651.

The capacitor C3A is formed of the conductor layers 621 and 653, and thedielectric layers 62 to 64 interposed between the conductor layers 621and 653. The capacitor C3B is formed of the conductor layers 621 and654, and the dielectric layers 62 to 64 interposed between the conductorlayers 621 and 654.

The capacitor C4A is formed of the conductor layers 621 and 642, and thedielectric layers 62 and 63 interposed between the conductor layers 621and 642. The capacitor C4B is formed of the conductor layers 621 and643, and the dielectric layers 62 and 63 interposed between theconductor layers 621 and 643.

The capacitor C11 is formed of the conductor layers 691 and 701, thedielectric layer 69 interposed between the conductor layers 691 and 701.The capacitor C12 is formed of the conductor layers 651 and 661, and thedielectric layer 65 interposed between the conductor layers 651 and 661.

The capacitor C23A is formed of the conductor layers 631, 641, 651 and653, and the dielectric layers 63 and 64 interposed between theconductor layers 631 and 651, and the dielectric layer 64 interposedbetween the conductor layers 641 and 651.

The capacitor C34A is formed of the conductor layers 623 and 653, andthe dielectric layer 64 interposed between the conductor layers 642 and653. The capacitor C34B is formed of the conductor layers 643 and 654,and the dielectric layer 64 interposed between the conductor layers 643and 654.

Next, structural features of the band-pass filter 101 will be describedwith reference to FIG. 24 . In the present embodiment, the distancebetween the second resonator 22 and the third resonator 23 is shorterthan that between the first resonator 21 and the second resonator 22,and is also shorter than that between the third resonator 23 and thefourth resonator 24. In the present embodiment, the distance between thesecond resonator 22 and the third resonator 23 is longer than thatbetween the second resonator 22 and the third resonator 23 in the firstembodiment (refer to FIG. 4 ).

As shown in FIG. 30A, the resonator-forming conductor layer 771 formedin the dielectric layer 77 and the resonator-forming conductor layer 771formed in the dielectric layer 78 are located so as to overlap eachother when viewed from the Z direction. As shown in FIGS. 31A and 31Bthe resonator-forming conductor layer 811 formed in the dielectric layer81 and the resonator-forming conductor layer 821 formed in thedielectric layer 82 are located so as to overlap each other when viewedfrom the Z direction. As shown in FIGS. 32A and 32B, theresonator-forming conductor layer 832 formed in the dielectric layer 83and the resonator-forming conductor layer 842 formed in the dielectriclayer 84 are located so as to overlap each other when viewed from the Zdirection. The resonator-forming conductor layer 833 formed in thedielectric layer 83 and the resonator-forming conductor layer 843 formedin the dielectric layer 84 are located so as to overlap each other whenviewed from the Z direction.

The operation and effects of the band-pass filter 101 according to thefirst embodiment will now be described. In the present embodiment, justas with the first embodiment, an attenuation pole at which insertionloss abruptly varies is formed in each of a first vicinity range that isa frequency range lower than a pass band and in the vicinity of the passband and a second vicinity range that is a frequency range higher thanthe pass band and in the vicinity of the pass band.

Specifically in the present embodiment, since the distance between thesecond resonator 22 and the third resonator 23 is made longer than thatof the first embodiment, the capacitive coupling between the secondresonator 22 and the third resonator 23 is weakened as compared to thecase of the first embodiment while the magnetic coupling between thesecond resonator 22 and the third resonator 23 is weakened as comparedto the case of the first embodiment. To be more specific, by providingno capacitor C23B, the capacitive coupling between the second resonator22 and the third resonator 23 is weakened. The capacitive couplingbetween the second resonator 22 and the third resonator 23 is adjustedby the capacitor C23A. On the other hand, in the first embodiment, thecapacitive coupling between the second resonator 22 and the thirdresonator 23 is adjusted by the capacitors C23A and C23B. According tothe present embodiment, as compared to the first embodiment, thecapacitive coupling between the second resonator 22 and the thirdresonator 23 is easily adjusted.

Next, examples of characteristics of the band-pass filter 101 accordingto the present embodiment will be described with reference to FIGS. 33to 38 . Here, the examples of characteristics of the band-pass filter101 that is designed such that the pass band includes a frequency bandof 4.7 GHz to 5.1 GHz will be described.

FIG. 33 shows an example of pass characteristic of the band-pass filter1, FIG. 34 shows part of FIG. 33 on an enlarged scale. Here, theinsertion loss when an unbalanced signal was inputted to the unbalancedport 11 is indicated as the pass characteristic of the band-pass filter101. In each of FIGS. 33 and 34 , the horizontal axis representsfrequency, and the vertical axis represents insertion loss. It is foundfrom FIG. 33 that in the band-pass filter 101, an attenuation pole atwhich the insertion loss abruptly varies is formed in each of first andsecond vicinity ranges.

By comparison between FIG. 33 and FIG. 17 , which shows an example ofpass characteristic of the band-pass filter 1 according to the firstembodiment, the following difference can be seen. In the band-passfilter 101, the attenuation pole formed in the higher-side frequencyrange is far from the pass band, as compared to the case of theband-pass filter 1. This is because of weakening of the capacitivecoupling between the second resonator 22 and the third resonator 23 bythe capacitors C23A and C23B as compared to the capacitive coupling ofthe band-pass filter 1, with weakening of the magnetic coupling betweenthe second resonator 22 and the third resonator 23 as compared to themagnetic coupling of the band-pass filter 1, by making the distancebetween the second resonator 22 and the third resonator 23 longer in theband-pass filter 101 than in the band-pass filter 1. In other words, ascan be seen from FIGS. 17 and 33 , strengthening of the capacitivecoupling between the second resonator 22 and the third resonator 23 withstrengthening of the magnetic coupling between the second resonator 22and the third resonator 23, by making the distance between the secondresonator 22 and the third resonator 23 shorter, allows the frequency ofthe attenuation pole formed in the second vicinity range to get closerto the pass band.

The insertion loss is preferably 3.0 dB or less. As shown in FIG. 34 ,the band-pass filter 101 has the insertion loss of 3.0 dB or less in theforegoing frequency bands.

FIG. 35 shows an example of amplitude balance characteristic of theband-pass filter 101. Here, the amplitude balance characteristic of theband-pass filter 101 is represented by using an amplitude difference,just as with FIG. 19 of the first embodiment. In FIG. 35 , thehorizontal axis represents frequency, and the vertical axis representsamplitude difference. With the amplitude difference denoted as m (dB), mpreferably has a value of −1.5 or more and not more than 1.5, and morepreferably −1.0 or more and not more than 1.0. As shown in FIG. 35 , theband-pass filter 101 has an m value of −1.0 or more and not more than1.0 in the foregoing frequency band.

FIG. 36 shows an example of phase balance characteristic of theband-pass filter 101. Here, the phase balance characteristic of theband-pass filter 101 is represented by using a phase difference, just aswith FIG. 20 of the first embodiment. In FIG. 36 , the horizontal axisrepresents frequency, and the vertical axis represents phase difference.With the phase difference denoted as p (deg), p preferably has a valueof 165 or more and not more than 196. As shown in FIG. 35 , theband-pass filter 101 has a p value of 165 or more and not more than 195in the foregoing frequency band.

FIG. 37 shows an example of reflection characteristic of the unbalancedport 11 of the band-pass filter 101. FIG. 38 shows an example ofreflection characteristic of the first and second balanced ports 12 and13 of the band-pass filter 101. In each of FIGS. 37 and 38 , thehorizontal axis represents frequency, and the vertical axis representsreturn loss. The return loss is preferably 10 dB or more. As shown inFIGS. 37 and 38 , the band-pass filter 101 has the return loss of 10 dBor more in the foregoing frequency band.

As described above, the band-pass filter 101 having the characteristicsshown in FIGS. 33 to 38 is usable in at least the frequency band of 4.7GHz to 5.1 GHz, and has the favorable balance characteristics in thisfrequency band. As is understood from FIGS. 33 to 38 , the band-passfilter 101 can form the abrupt attenuation pole in each of the first andsecond vicinity ranges while satisfying the balance characteristics.

The configuration, function and effects of the present embodiment areotherwise the same as those of the first embodiment.

Third Embodiment

A third embodiment of the invention will now be described. First, thecircuit configuration of a band-pass filter according to the presentembodiment will be described in brief with reference to FIG. 39 . FIG.39 shows the circuit configuration of the band-pass filter according tothe present embodiment.

The circuit configuration of a band-pass filter 201 according to thepresent embodiment is different from that of the band-pass filter 101according to the second embodiment in the following respect. In thepresent embodiment, there is no capacitor C23A provided for connectingone end of the second resonator 22 on the side of the capacitor C2A toone end of the third resonator 23 on the side of the capacitor C3A.

The band-pass filter 201 includes capacitors C5A and C5B. Each of thecapacitors C5A and C5B has a first end and a second end. The first endof the capacitor C5A is connected to the capacitors C2A and C3A. Thesecond end of the capacitor C5A is connected to the ground.

The first end of the capacitor C5B is connected to the capacitors C2Band C3B. The second end of the capacitor C5B is connected to the ground.

The other circuit configuration of the band-pass filter 201 is the sameas that of the band-pass filter 101 according to the second embodiment.

In the present embodiment, each of a group of the capacitors C2A, C3A,and CSA and a group of the capacitors C2B, C3B, and C5B are connected inso-called. Y-shaped connection. Therefore, according to the presentembodiment, it is possible to reduce the capacitance of each of thecapacitors C2A, C2B, C3A, C5B, C5A, and C5B, as compared with a casewhere these groups are connected in so-called π-shaped connection orΔ-shaped connection. As a result, the present embodiment allowsdownsizing of the band-pass filter 201.

The configuration, function and effects of the present embodiment areotherwise the same as those of the second embodiment.

The present invention is not limited to the foregoing embodiments, andvarious modifications may be made thereto. For example, the band-passfilter according to the present invention may be integrated with anothercircuit into a stack electronic component. Examples of the othercircuits include a branch circuit, a filter, and a matching circuit.

Obviously, many modifications and variations of the present invention apossible in the light of the above teachings. Thus, it is to beunderstood that, within the scope of the appended claims and equivalentsthereof, the invention may be practiced in other embodiments than theforegoing most preferable embodiments.

What is claimed is:
 1. A band-pass filter comprising: an unbalancedport; a first balanced port; a second balanced port; a first resonatorprovided between the unbalanced port and the first and second balancedports in a circuit configuration; a second resonator provided betweenthe first resonator and the first and second balanced ports in thecircuit configuration; a first capacitor connecting one end of the firstresonator to a ground; a second capacitor connecting one end of thesecond resonator to the ground; and a third capacitor connecting anotherend of the second resonator to the ground, wherein the first resonatoris jump-coupled to the second resonator by magnetic coupling.
 2. Theband-pass filter according to claim 1 further comprising a stackincluding a plurality of stacked dielectric layers, a plurality ofstacked conductor layers, and a plurality of through holes, wherein theplurality of conductor layers include a plurality of resonator-formingconductor layers, the plurality of through holes include a plurality ofresonator-forming through holes, the second resonator includes a firstthrough hole line, a second through hole line, and a conductor layerportion, each of the first and second through hole lines is formed ofserially connected two or more through holes of the plurality ofresonator-forming through holes, and penetrates two or more dielectriclayers of the plurality of dielectric layers, and the conductor layerportion is formed of one or more resonator-forming conductor layers ofthe plurality of resonator-forming conductor layers, and connects oneend of the first through hole line to one end of the second through holeline.
 3. The band-pass filter according to claim 1 further comprising athird resonator provided between the first resonator and the secondresonator in the circuit configuration.
 4. The band-pass filteraccording to claim 3, wherein the first resonator and the thirdresonator are capacitively coupled through a capacitor.
 5. The band-passfilter according to claim 3 further comprising: a fourth capacitorconnecting one end of the third resonator to the ground; and a fifthcapacitor connecting another end of the third resonator to the ground.6. The band-pass filter according to claim 5 further comprising a sixthcapacitor connecting each one end of the second and fourth capacitors tothe ground.
 7. The band-pass filter according to claim 3, wherein adistance between the second resonator and the third resonator is shorterthan a distance between the first resonator and the third resonator. 8.The band-pass filter according to claim 3 further comprising a fourthresonator provided between the second resonator and the first and secondbalanced ports in the circuit configuration, wherein the fourthresonator is jump-coupled to the third resonator.
 9. The band-passfilter according to claim 8 further comprising: a fourth capacitorconnecting one end of the third resonator to the ground; a fifthcapacitor connecting another end of the third resonator to the ground; aseventh capacitor connecting one end of the fourth resonator to theground; and an eighth capacitor connecting another end of the fourthresonator to the ground, wherein another end of the first resonator isconnected to the ground.
 10. The band-pass filter according to claim 8,wherein a distance between the second resonator and the third resonatoris shorter than a distance between the first resonator and the thirdresonator, and shorter than a distance between the second resonator andthe fourth resonator.
 11. A band-pass filter comprising: an unbalancedport; a first balanced port; a second balanced port; a first resonatorprovided between the unbalanced port and the first and second balancedports in a circuit configuration; a second resonator provided betweenthe first resonator and the first and second balanced ports in thecircuit configuration; a third resonator provided between the firstresonator and the second resonator in the circuit configuration; a firstcapacitor connecting one end of the first resonator to a ground; asecond capacitor connecting one end of the second resonator to theground; and a third capacitor connecting another end of the secondresonator to the ground, wherein a distance between the second resonatorand the third resonator is shorter than a distance between the firstresonator and the third resonator.
 12. A band-pass filter comprising: anunbalanced port; a first balanced port; a second balanced port; a firstresonator provided between the unbalanced port and the first and secondbalanced ports in a circuit configuration; a second resonator providedbetween the first resonator and the first and second balanced ports inthe circuit configuration; a third resonator provided between the firstresonator and the second resonator in the circuit configuration; afourth resonator provided between the second resonator and the first andsecond balanced ports in the circuit configuration; a first capacitorconnecting one end of the first resonator to a ground; a secondcapacitor connecting one end of the second resonator to the ground; anda third capacitor connecting another end of the second resonator to theground, wherein the fourth resonator is jump-coupled to the thirdresonator.
 13. The band-pass filter according to claim 12, wherein thejump-coupling is by magnetic coupling.